<!DOCTYPE html>

<html>
<head>
    <style>
        #resizing {
            width: 400px;
            border: 1px solid black;
        }

        #resizing > div {
            height: 50px;
            margin: 1px;
            background-color: silver;
        }
    </style>
</head>
<body>

<div id="resizing">
  <div></div>
  <div></div>
  <div></div>
  <div></div>
</div>

</body>
</html>
